This application is submitted in the name of the following inventor:
1. Field of the Invention
This invention relates to dynamic adaptation of link parameters for wireless communication. In particular, the invention relates to dynamic adaptation of link parameters such as modulation scheme, symbol rate, and error correction scheme for a wireless communication link.
2. Description of the Related Art
Conventional wireless communication systems adapt their modulation schemes based on periodic measurements of channel quality. A measurement of channel quality used by these systems is a bit error rate (BER) statistic. These conventional systems have several drawbacks.
First, different modulation schemes can have radically different throughput efficiencies and error tolerances. As a result, a change in modulation schemes to accommodate an increase in communication errors can result in an unacceptable decrease in throughput efficiency.
Second, BER statistics take some time to change in order to reflect an increase in communication errors. The periodic nature of BER statistic computations exacerbates this problem. In particular, a change in a rate of communication errors is not reflected in the BER statistics until an end of a period. If the error rate changes near the end of the period, the BER statistics may not reflect the change until the end of the next period. During this delay, a modulation scheme with unacceptable error tolerance may be utilized, adversely impacting communication over a wireless link.
Accordingly, what is needed is a system of dynamically adapting a set of wireless link parameters that provides a better selection of throughput versus error tolerance options and that adapts more efficiently to changes in communication error rates.
One embodiment of the present invention that addresses the foregoing need is a method of dynamically adapting wireless link parameters. A measure is determined of errors occurring in communication over a wireless link. In a case that the measure of errors corresponds to more errors than a first predetermined threshold, communication changes from a first set of wireless link parameters to a second set of wireless link parameters. The second set of wireless link parameters corresponds to higher error tolerance than the first set of wireless link parameters. In a case that the measure of errors corresponds to fewer errors than a second predetermined threshold, communication changes from the first set of wireless link parameters to a third set of wireless link parameters. The third set of wireless link parameters corresponds to lower error tolerance than the first set of wireless link parameters.
By utilizing at least three sets of wireless link parameters, the invention provides greater flexibility for adapting to changes in communication error rates.
Preferably, the measure of errors is determined by monitoring a number of NACK messages and a number of ACK messages that occur. It is determined that the measure of errors corresponds to more errors than the first predetermined threshold when more than a predetermined number of NACK messages occur in succession. It is determined that the measure of errors corresponds to fewer errors than the second predetermined threshold when more than a predetermined number of ACK messages occur in succession.
The foregoing monitoring for successive NACK and ACK messages can occur continuously. As a result, adaptation of wireless link parameters can occur as soon as a successive number of NACK or ACK messages is received, allowing for more rapid and efficient adaptation to communication conditions.
Each set of wireless link parameters can include a modulation scheme, a symbol rate, and/or an error correction scheme. In a preferred embodiment, each set of wireless link parameters includes Quadrature Amplitude Modulation or Quadrature Phase Shift Keying, high symbol rate or low symbol rate, and high forward error correction or low forward error correction.
The foregoing sets of parameters have been found to provide good flexibility for adapting communication over a wireless link to accommodate various error rates. Other parameters may be utilized, possibly but not necessarily including the foregoing parameters.
Each set of wireless link parameters corresponds to a relationship between throughput efficiency and error tolerance. The first predetermined threshold preferably corresponds to where the relationship for the first set of wireless link parameters intersects the relationship for the second set of wireless link parameters. The second predetermined threshold preferably corresponds to where the relationship for the first set of wireless link parameters intersects the relationship for the third set of wireless link parameters.
An optimal set of parameters tends to be automatically selected for a given error rate by using theses intersections as thresholds for changing between sets of parameters.
The invention also can be embodied in communication systems, communication hardware, MMDS head ends, and software for controlling MMDS communication that utilizes the foregoing methods. Other embodiments of the invention are possible.
By virtue of the foregoing arrangements, the invention provides a better selection of throughput versus error tolerance options and adapts more efficiently to changes in communication error rates.